ORGANIZATION. 
43 
are required, as saliva, gastric juice, and bile: these are 
secreted by special organs, called glands. Moreover, since 
not all the food eaten is fitted to make blood, and as the 
blood itself, in going around the body, acts like a scaven¬ 
ger, picking up worn-out particles, we have another func¬ 
tion, that of excretion, or removal of useless matter from 
the system. The kidneys and lungs do much of this; but 
the lungs do something else. They expose the blood to 
the air, and introduce oxygen, which, we shall find, is 
essential to the life of every animal. 
These centripetal and centrifugal movements in the 
body—throwing in and throwing out—are so related and 
involved, especially in the lower forms, that they cannot 
be sharply defined and classified. It has been said that 
every Dog has two lives — a vegetative and an animal. 
The former includes the processes of digestion, circulation, 
respiration, secretion, etc., which are common to all life; 
the functions of the other, as motion, sensation, and will, 
are peculiar to animals. The heart is the centre of the 
vegetative life, and the brain is the centre of the animal 
life. The aim of the vegetative organs is to nourish the 
individual, and reproduce its kind; the organs of locomo¬ 
tion and sense establish relations between the individual 
and the w T orld without. The former maintain life; the 
others express it. The former develop, and afterwards 
sustain, the latter. The vegetative organs, however, are 
not independent of the animal; for without muscles and 
nerves we could not procure, masticate, and digest food. 
The closer the connection and dependence between these 
two sets of organs, the higher the rank. 18 
All the apparatus and phenomena of life may be in* 
eluded under the heads of 
Nutrition, 
Motion, 
Sensation. 
Reproduction. 
